1. Field of the Invention
The present disclosure relates to a method for measuring spreading resistance by measuring a two-dimensional spreading current distribution of a sample using a scanning probe microscope and to a spreading resistance microscope.
2. Description of the Related Art
Recently, a scanning spreading resistance microscope (SSRM) has been developed in which a two-dimensional resistance distribution is obtained using a scanning probe microscope by bringing a conductive probe into contact with a surface of a sample, applying a bias voltage thereto, and measuring a current flowing through the probe using a wide range logarithmic amplifier (see, for example, JP-A-2008-002952).
In the SSRM, by scanning a surface of a sample with a probe with a voltage applied between the surface of the sample and the probe and detecting height information of the surface of the sample and a current flowing through the probe, a concave-convex shape of the sample and two-dimensional spreading resistance just below the probe can be acquired at the same time. When a bias voltage is applied to the sample, only carriers positioned in the vicinity just below the probe flow into the probe, and a current flows and local resistance which is obtained by converting the voltage and the current into a resistance value is referred to as spreading resistance. In this way, since the applied voltage is concentrated on just below the probe in the SSRM, a current (spreading resistance) with which a dopant concentration is dominant just below the probe can be detected, this technique is anticipated as being capable of measuring a dopant concentration distribution of semiconductor.
Incidentally, similarly to an atomic force microscope (AFM), the SSRM glidingly scans the sample surface while bringing the probe into contact with the surface, and sequentially detects a current (resistance) when the probe reaches a predetermined detection position on an XY plane of the sample. However, since the current is measured while continuously changing the position at which the probe is in contact with the sample, as illustrated in FIG. 5, the current value is not stable due to unstable contact resistance of a contact. Therefore, in order to stabilize the contact resistance, current measurement may also be performed by pressing the probe with a predetermined load.
When measuring spreading resistance of the sample, unintended oxide may be formed on the surface of the sample. For example, when spreading resistance of a Si wafer is measured under atmospheric gas, the sample surface is oxidized to form an oxide during placing the wafer in the SSRM or during measurement. When a current is measured by pressing the probe on the sample with an oxide formed on the surface thereof, the probe strips the oxide into fragments and drags the fragments as they are. For this reason, as illustrated in FIG. 6, sometimes stripe-shaped measurement noise occurs in an image of a spreading resistance distribution.
The wafer of which the surface is oxidized is once removed from the SSRM and the oxide is removed under hydrofluoric acid treatment, mechanical polishing, or the like, and then measurement is performed again. However, measurement efficiency decreases due to replacement of the sample or the sample surface is sometimes oxidized again between oxide removal and measurement.
In the SSRM according to the related art, since current is measured while moving the probe, an average resistance value of a large area including a measurement point in addition to the measurement point representing a detection position is acquired. For this reason, similarly, there may be a problem that measurement noises occur or accurate spreading resistance cannot be obtained due to the dragging of fragments.